Several approaches have been taken toward enhancing growth and feed utilization in food animals. These approaches, which include the use of antibiotics and biological compounds such as growth hormones and growth hormone releasing factors, have either unacceptable side effects, public health consequences, a social stigma, or they are too expensive for producers to implement profitably. Antibiotic supplementation has been used to treat diseases, enhance feed utilization, and to otherwise benefit the health and/or metabolism of food producing animals. The use of antibiotics allows greater production from animals (e.g., in the form of meat, eggs and milk) from the same quantity of feed, thus allowing greater potential for profitability. However, as awareness has increased to the potential danger of resistance to antibiotics used in the treatment of people, there has been growing pressure from consumers and governmental authorities to avoid using such antibiotics as feed additives in animals. Indeed, as a result of increasing consumer pressure and in particular concerns about increased microbial resistance to antibiotics, a ban on the use of antibiotic growth promoters in animal feed has already been introduced in Germany. In 1998, the European Union banned antibiotics important in human medicine from use as growth promoters in livestock production.
There is considerable evidence that the development of resistant organisms is reducing the number of effective antibiotics available for doctors to treat bacterial infections successfully. The more microorganisms that become resistant to antibiotics, the greater the risk of a resurgence of untreatable infectious diseases. The overuse of antibiotics in livestock feed is believed to be a major factor contributing to the increase in antibiotic resistance. A majority of the antibiotics used in animal husbandry today are not used to treat sick animals, but rather to promote more efficient growth and utilization of feed.
Used properly, subtherapeutic administration of antimicrobials and antibiotics as feed supplements in farm animals increases production of meat and milk per pound of food fed and enables producers to provide consumers with a lower-cost product. By reducing the risk of outbreak of some diseases, and enhancing growth rates and feed efficiency, the use of these agents allows animals to grow bigger faster. The effect on growth may be due to suppression of harmful bacteria in the digestive tract, which helps maintain the proper absorption of nutrients. The administration of subtherapeutic levels of antibiotics also may exert a modulating effect on the metabolic activity of certain intestinal bacteria or it may shift the balance of the microbial ecosystem, which constitutes an essential part of digestion. The positive effects may also be due to the antibiotics killing or inhibiting the growth of organisms that would otherwise make the animals ill. Animals that are ill generally do not eat properly and their growth rate and overall health therefore diminish.
Thus, there is a need for methods of enhancing the growth and feed efficiency of animals by administering or feeding antibiotics that are not traditionally used in medicine to treat bacterial infections, thus decreasing the danger of increasing resistance to those traditional antibiotics. There is also a need for animal feedstuffs containing antibiotics that will enhance the physical performance of animals while not adding to the problem of increasing bacterial resistance to medically useful antibiotics. The present invention meets these needs.